1. Field of the Invention
Embodiments of the present invention generally relate to computer graphics and, more specifically, to techniques for conflating raster and vector data.
2. Description of the Related Art
Conventional digital images are generally represented in either vector or raster formats. Raster graphics, also called bitmap graphics, consist of a sequence of data representing a generally rectangular grid of picture elements, called pixels. Raster graphics generally correspond pixel-for-pixel with a displayed or printed representation of the content. Because raster graphics are discrete, they generally do not scale well.
Raster formats are used to store arrays of pixel color values, the color values specifying a color for each pixel location within a rectangular array of pixels. Raster images are generally resolution dependent, and the information in a raster image file only suffices to identify color values for a fixed resolution. Raster images can be scaled down in size by down-sampling such as by averaging, and scaled up by up-sampling such as by interpolation. However, up-sampled color values in general are artificial, and often destroy the true nature of an image. Familiar examples of raster images include image images acquired by a digital camera or scanner.
Vector graphics, on the other hand, are represented by description, rather than by listing a value for each pixel in a graphic. Geometric shapes can be represented as a vector graphic, and an arbitrary shape may be represented by a combination of such geometric shapes. For instance, a straight-line segment can be described as a vector graphic by describing its two endpoints, or by its slope, length, and origin. Likewise, a circle can be described in vector representation by describing its radius and center point. Accordingly, vector graphics are sometimes referred to as geometric data since they define objects by description rather than as a sequence of pixels. Because vector graphics are continuous, they can scale well. Familiar examples of vector images include flowcharts, block diagrams and other synthetic images produced by graphics software applications.
Image compositing involves generation of complex images by overlaying simpler images on top of one another. For example, a composite image may include a layer for a background, layers for various sprites, and a layer for text. Layers are generally arranged one on top of another. One of the many challenges of image compositing is the overlaying of raster and vector images. Since vector images are generally resolution independent, conventional digital compositing systems scale a vector image to the pixel dimensions of a raster image, when overlaying one upon the other.
Many organizations, e.g., utilities such as electric, gas, and telecom utilities, maintain data in what are sometimes call hybrid maps that are a composite image of raster and vector information resulting from a conflation process. For example, raster maps include scanned maps and/or rasterized results of vector maps. Vector maps may include maps with facilities or landbase features that are represented as vector graphics layers. The hybrid maps, therefore, contain overlapping data from both types of maps. It has been observed, however, that current methods of conflating such hybrid maps result in inaccuracies that can present hazards for field operations. For example, it is an undesirable result to visually misrepresent connections of electric conductors in a hybrid map. Indeed, such a misrepresented connection can result in costly errors and may present safety issues.
As the foregoing illustrates, there is a need in the art for a robust and practical approach for aligning raster and vector data across varying environments.